1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine.
2. Description of the Related Art
In recent years, there has been a demand for the image forming apparatus to shorten a first print out time (hereinafter, abbreviated as a FPOT), which indicates a time elapsing until the first sheet of a recording material is discharged after receiving a request to form an image. The FPOT largely depends on a time elapsing until a fixing device reaches a fixable temperature after receiving the request to form the image (hereinafter, referred to as a rising time).
Meanwhile, in order to cope with the colorization and speeding-up of an image forming apparatus, an inline-type color image forming apparatus has been developed. In the inline-type image forming apparatus, a plurality of photosensitive drums is mounted. Toner images with different colors are formed on the respective photosensitive drums, sequentially overlaid with each other on an intermediate transfer belt, and then collectively transferred onto a recording material. Alternatively, the toner images on the photosensitive drums are sequentially overlaid on the recording material which is disposed on a transfer belt.
In the case of an inline-type color image forming apparatus, a time elapsing until the recording material reaches the fixing device after starting the formation of the image on a first photosensitive drum is long. Japanese Patent No. 3265853 discusses the apparatus in which, when a time necessary for the fixing device to reach a fixing temperature calculated from a temperature rising rate of a heater is shorter than a time necessary for the recording material to reach the fixing device, the recording material starts to be fed immediately after the temperature rising rate is measured. In contrast, when the time necessary for the fixing device to reach the fixing temperature is longer than the time necessary for the recording material to reach the fixing device, the feeding of the recording material is to be delayed.
In order to shorten the FPOT, it is necessary to supply more power to the fixing device and determine, when the fixing device is at a lower temperature, whether “to start the formation of an image”. The apparatus discussed in Japanese Patent No. 3265853 is effective in setting the timing of sheet feeding. However, since the timing of sheet feeding is determined based on temperature change information of the fixing device, there is a limitation in shortening the FPOT.